Mechanisms of the Time-varying Sea Level and Heat Content Trend in the Eastern Nordic Seas

Sara Broomé1, Leon Chafik1 and Johan Nilsson2, (1)Stockholm University, Department of Meteorology, Stockholm, Sweden, (2)Stockholm University, Department of meteorology, Stockholm, Sweden
The Nordic Seas is the main ocean conveyor of heat between the North Atlantic Ocean and the Arctic Ocean. Although the decadal variability of the Subpolar North Atlantic has been given significant attention lately, especially regarding the cooling trend since the mid-2000s, less is known about the potential connection there might be downstream in the northern basins. Using the satellite altimetry record of sea surface heights, we find significant variability on multiyear-to-decadal time scales in the Nordic Seas. In particular, and on top of a general positive trend due to global sea level rise, regional trends in sea surface heights show signs of a slowdown since the mid-2000s as compared to the rapid increase in the preceding decade. This change is most prominent in the Atlantic origin waters in the eastern Nordic Seas and is closely linked, as estimated from hydrography, to heat content.
We formulate a simple heat budget for the eastern Nordic Seas to discuss the relative importance of local and remote sources of variability; advection of temperature anomalies in the Atlantic inflow is found to be the main mechanism. A conceptual model, with only upstream temperature measurements at the inflow to the Nordic Seas as input, is able to reproduce aspects of the decadal variability of the Nordic Seas' heat content.
Based on these results, we argue that there is a strong connection between the upstream Subpolar North Atlantic and the Nordic Seas. However, although the timing of the changes in trends in the Nordic Seas and Subpolar North Atlantic is remarkably coincident, the connection is not uncomplicated; while the Subpolar North Atlantic have experienced a reversal of trends, the eastern Nordic Seas have only seen a stagnation.